A Long-Term Evolution (LTE) system, an LTE-Advance (LTE-A) system and an International Mobile Telecommunication Advanced (IMT-A) system are all based on Orthogonal Frequency Division Multiplexing (OFDM). In an OFDM system, data are in a form of two dimensions, i.e., time domain and frequency domain. In the OFDM system, one subframe consists of two slots. If adopting a normal Cyclic Prefix (CP), each slot consists of seven OFDM symbols; and if adopting an extended CP, each slot consists of six OFDM symbols. A Physical Downlink Control Channel (PDCCH) is located on the former one or two or three or four OFDM symbols. In an LTE communication system, the information transmitted by the PDCCH consists of Downlink grant (DL grant) information and Uplink grant (UL grant) information.
At present, in the LTE system, a mapping process of the PDCCH is that: at a transmission end, an Enhanced NodeB (eNB) first encodes the PDCCH (comprising DL grant and UL grant) of each piece of User Equipment (UE) belonging to the eNB independently, that is, the PDCCH of each UE can adopt a different code rate; then the eNB concentrates all encoded PDCCHs in series and scrambles them using a cell-specific sequence to obtain a series of Control Channel Elements (CCEs); later the eNB performs Quadrature Phase Shift Keying (QPSK) modulation on the series of CCEs above, and then interleaves the symbols above with a Resource Element Group (REG) as a unit and finally maps the symbols to the former one or two or three or four OFDM symbols in a manner of first time domain and then frequency domain. At a receiving end, the UE demodulates the PDCCH using Cell-Specific Reference Signals (CRSs) and performs blind detection on the CCE to finally obtain respective PDCCH.
FIG. 1 shows an architecture diagram of a mobile communication system introducing a relay node. In the mobile communication system, a link between an eNB and a Relay Node (RN) is called a relay link (backhaul Link or Un link); a link between the RN and a user in the coverage of the RN is called an access link (or Uu link); and a link between the eNB and a UE in the coverage of the eNB is called a direct link. For the eNB, an RN equals a UE; for the UE, the RN equals an eNB.
So called inband relay means that the backhaul link and the access link use the same frequency band. Therefore, when inband relay is adopted, in order to avoid the transmission-receiving interference of the RN itself, the RN can not perform transmission and receiving simultaneously on the same frequency resource. When the RN transmits a physical downlink control channel to a UE belonging to the RN, the RN can not receive a physical downlink control channel from the eNB. Therefore, on a downlink backhaul subframe (that is, the subframe on which the eNB transmits data to the RN), the RN first transmits a PDCCH to the UE belonging to the RN on the former one or two OFDM symbols, and then performs handover from transmission to receiving in a time period, after handover is completed, the RN receives data from the eNB on the latter OFDM symbols, the data comprising an R-PDCCH and a Physical Downlink Shared Channel (PDSCH) of the relay, as shown in FIG. 2.
The R-PDCCH transmitted from the eNB to the RN is borne on a Physical Resource Block (PRB), the R-PDCCH comprising information such as uplink/downlink scheduling grant of the RN. On a downlink backhaul subframe, as shown in FIG. 3, the eNB semi-statically reserves a number of PRBs for transmission of the R-PDCCH. The inventor finds that in relevant art there is no reasonable mapping solution when bearing the R-PDCCH using the PRBs, thus resource conflict or overflow might be caused and backhaul resources can not be effectively utilized.